1. Field of the Invention
The present invention relates to a digital broadcast transmitting method and a digital broadcast transmitting apparatus suitable for a system that repeats a digital satellite broadcast program with a digital CATV (community Antenna Television).
2. Description of the Related Art
An analog CATV often receives and repeats satellite broadcast programs as CATV programs. When a satellite broadcast program is repeated and delivered as an analog CATV channel program, a video signal and an audio signal are demodulated from a satellite broadcast signal. The demodulated video and audio signals are modulated with a predetermined carrier. The modulated signal is transmitted as a CATV program signal.
A digital CATV is being developed as a successor of the analog CATV. At present, instead of analog satellite broadcasts, digital satellite broadcasts are becoming common. Thus, with the digital CATV, digital satellite broadcast programs are received and delivered.
In both the digital CATV and digital satellite broadcast, data is transmitted with a stream corresponding to MPEG (Moving Picture Experts Group) 2. In other words, both the digital CATV and digital satellite broadcast use the same encoding method. Thus, when the digital CATV delivers a digital satellite broadcast signal, it is not necessary to decode video data and audio data. Instead, only the conversion of the modulating method is required.
In other words, in the digital CATV, a digital video signal is compressed corresponding to MPEG2 and modulated corresponding to for example QAM (Quadrature Amplitude Modulation). The modulated signal is transmitted with a predetermined carrier through a cable. On the other hand, in the digital satellite broadcast, a digital video signal is compressed corresponding to for example MPEG2 and modulated corresponding to for example QPSK (Quadrature Phase Shift keying). The modulated signal is transmitted with a 12 GHz band radio wave through a satellite.
Thus, although the digital CATV and the digital satellite broadcast use the same encoding method that is MPEG2, they use different modulating methods. Consequently, when a signal that has been demodulated corresponding to QPSK is modulated corresponding to QAM, a digital satellite broadcast program can be delivered with a digital CATV.
When a digital satellite broadcast program is delivered with a digital CATV, only the conversion of the modulating method is required. However, when the modulating method of a digital satellite broadcast program is converted and the converted program is delivered with a digital CATV, the management company of the digital CATV will have difficulties for managing subscription contracts and charging operations thereof.
In other words, when a person wants to subscribe to a CATV program, he or she should make a subscription contract with the management company of the CATV broadcast. The management company will manage a subscription contract with the person and a charging operation thereof. To manage the subscription contracts and charging operations, the digital CATV system should perform scrambling operations so that only subscribers can receive CATV programs. Thus, in addition to the conversion of the modulating method, the digital CATV system should scramble a received digital satellite broadcast signal corresponding to suscription contracts for subscribers and transmit the scrambled signal to the subscribers.
Thus, when the management company of the CATV manages subscription contracts and charging operations thereof, it should perform the scrambling operations in addition to the conversion of the modulating method. Consequently, the processes performed on the digital CATV system side become complicated. Thus, the cost of the system becomes high.
Therefore, an object of the present invention is to provide a digital broadcast transmitting method and a digital broadcast transmitting apparatus that allow a digital CATV system that repeats and delivers a digital satellite broadcast program to manage subscription contracts and charging operations in a simple structure at low cost.
A first aspect of the present invention is a digital broadcast transmitting method of a system having a first digital broadcast transmitter for supplying a broadcast program, a second digital broadcast transmitter for repeating and transmitting the broadcast program received from the first digital broadcast transmitter, and a receiving terminal for receiving the broadcast program from the second digital broadcast transmitter and reproducing the received broadcast program. The method compriser the steps of (a) transmitting individual information from a first digital broadcast transmitter to a second digital broadcast transmitter, (b) selecting particular individual information from the individual information received at the second digital broadcast transmitter and transmitting the selected individual information to a receiving terminal, (c) storing contract data corresponding to the particular individual information when it is assigned at the receiving terminal, (d) transmitting common information necessary for descrambling the broadcast program when it is scrambled and transmitted, (e) transmitting the scrambled broadcast program and the common information from the second digital broadcast transmitter to the receiving terminal, and descrambling the scrambled broadcast program using a descramble key corresponding to the common information when the contract data stored in the receiving terminal allows the descrambled broadcast program to be descrambled. terminal, (c) causing the receiving terminal to store contract data corresponding to the particular individual information when it is assigned to the receiving terminal, (d) causing the first digital broadcast transmitting means to transmit common information necessary for descrambling the broadcast program when it is scrambled and transmitted, (e) causing the second digital broadcast transmitting means to transmit the scrambled broadcast program and the common information to the receiving terminal, and (f) causing the receiving terminal to obtain a descramble key corresponding to the common information and descramble the scrambled broadcast program only when the contract data stored in the receiving terminal allows the descrambled broadcast program to be descrambled.
A second aspect of the present invention is a digital broadcast transmitting apparatus for repeating and transmitting a digital broadcast program to a receiving terminal. The digital broadcast transmitting apparatus comprises a receiver receiving the digital broadcast program, a demodulator for demodulating digital data of a signal received by the receiver, an individual information selector for selecting particular individual information from individual information of digital data that is output from the demodulator a manager for managing individual information selected by the individual information selector and a modulator for modulating delivery data. The CATY management company has a group of identification numbers.
The CATV management company has a group of identificatin numbers. When a digital satellite broadcast program is repeated and delivered with a digital CATV broadcast, one of identification numbers is assigned to each subscriber of the digital CATV. In the digital CATV broadcast, only EMM (Entitlement management message) information of the identification numbers belonging to subcribers are filtered and transmitted. Thus, without need to dispose a scrambling circuit on the digital CATV system side, the management company of the digital CATV system can manage subscription channels and charging operations thereof.